Partial session transfer method and user equipment for the same

ABSTRACT

A session transfer procedure not for all ongoing multimedia components but for some media components in a wireless communication system and an apparatus for the same are provided. In a partial session transfer procedure, a user equipment establishing a first session to transmit a plurality of media components transmits a partial attach request message to a mobility control entity of a network core. The partial attach request message may be an attach request message whose attach type is set to ‘partial handover’. Upon receiving an attach accept message containing information regarding a gateway of the network core from the mobility control entity, a second session is established with the gateway by using the gateway information. After the establishing of the second session, the user equipment does not release the previously established first session. The user equipment transmits partial session transfer information indicating a media component to be transmitted using each of the first session and the second session among the plurality of media components to a counterpart user equipment, and thereafter exchanges multimedia data with the counterpart user equipment through both of the first session and the second session on the basis of the partial session transfer information.

TECHNICAL FIELD

The present invention relates to wireless communications, and moreparticularly, to a session transfer procedure not for all ongoingmultimedia components but for some media components in a wirelesscommunication system and an apparatus for the same.

BACKGROUND ART

Multimedia service continuity has been introduced in 3^(rd) generationpartnership project (3GPP) release 8. The multimedia service continuityimplies that, when an access network (AN) changes or a user equipment(UE) used by a user changes, an ongoing multimedia session is continuedby using the changed AN or the changed UE. The multimedia servicecontinuity is provided to use a seamless multimedia service when the UEunder the multimedia service attempts access through another AN or whenthe user transfers media of the ongoing multimedia session to anotherUE.

Several scenarios have been introduced in association with themultimedia service continuity. Examples of the scenarios include ‘PS-PSsession continuity’ which denotes multimedia session continuity when amultimedia session is transferred between different packet switched (PS)ANs, ‘PS-PS session continuity in conjugation with PS-CS continuity’which denotes multimedia session continuity when media sessions on a PSdomain and a circuit switched (CS) domain are transferred to one PS AN,or the other way around, and ‘UE transfer’ which denotes sessioncontinuity when a media component is transferred between different UEscontrolled by the same user.

The scenarios in association with the multimedia service continuity maybe a procedure in which all or some of the ongoing multimedia componentsare transferred to another AN and/or another UE. According to the 3GPPrelease 8, ‘multimedia session transfer’ or simply ‘session transfer’ isdefined as transfer at an IP multimedia subsystem (IMS) level in sessionsignaling paths and media paths of an ongoing session while maintainingsession continuity.

The multimedia session transfer can be realized by AN transfer and/or UEtransfer. The AN transfer implies a change of an AN from a UE to an IMScore, that is, a change of a network core of a radio access network(RAN) (e.g., a base station (BS)) and/or an Internetprotocol-connectivity access network (IP-CAN). On the other hand, the UEtransfer implies session transfer between different UEs controlled bythe same user. For example, this is a case where all media components orsome media components of an ongoing multimedia session are transferredto any one of the UEs to another UE.

To achieve the multimedia service continuity, there is a methodemploying a session anchoring mechanism using the IMS core. Morespecifically, a specific application server for providing the multimediaservice continuity (e.g., a multimedia session continuity applicationserver (MMSC AS)) may be installed in the IMS core so that all ongoingcontrol signals and data signals are transmitted through the MMSC AS.Further, when there is a session transfer request, all or some mediacomponents of the ongoing multimedia session are allowed to pass throughanother AN with respect to the MMSC AC and/or are allowed to communicatewith another UE.

-   -   Advantageously, the session anchoring mechanism using the MMSC        AS can support the multimedia service continuity through session        transfer without having to significantly depend on an AN type, a        UE type, a media component characteristic, etc.        Disadvantageously, however, the mechanism is not much effective        since it is premised that control signals and data signals for        session transfer are delivered up to the IMS core, i.e., the        MMSC AS. An additional procedure (e.g., IMS registration) may be        required.

DISCLOSURE Technical Problem

The aforementioned multimedia service continuity can be achieved bytransferring a session between an AN to be accessed to an IMS coreand/or UEs under the premise that signaling is delivered to an MMSC AS,i.e., an application server of the IMS core. However, as describedabove, it is not effective to allow signaling to be always delivered toan IMS layer for session transfer. Therefore, if session transfer can beprovided in an IP layer or lower layers of the IP layer instead ofdelivering the signaling to an IMS layer, the multimedia servicecontinuity can be more effectively achieved.

For example, when the AN includes an evolved packet system (EPS), PS-PSsession connectivity can be supported through a handover proceduredisclosed in 3GPP TS 23.401 or 3GPP TS 23.402. Accordingly, signalingfor session transfer does not have to be delivered to the MMSC AC of theIMS core. Thus, a multimedia session can be transferred betweendifferent network cores and/or between different UEs through signalingat the IP level or the lower layers of the IP layer.

However, the aforementioned multimedia service continuity needs to beprovided not only when session transfer is performed for all ongoingmultimedia components but also when session transfer is performed forsome media components. When session transfer is performed for some mediacomponents, previous sessions for the remaining components may bereleased or maintained, which may differ depending on a situation. Assuch, when sessions for some media components are transferred to anotherAN and/or another UE, it is called ‘partial session transfer’. Theconventional handover procedure disclosed in 3GPP TS 23.401 and 3GPP TS23.402 assumes that session transfer is performed for all ongoingmultimedia components and does not consider the partial sessiontransfer.

Accordingly, the present invention provides a session transferprocedure, whereby multimedia service continuity can be achieved even ifsession transfer is performed not for all ongoing multimedia componentsbut for some media components, and a UE for the same.

The present invention also provides an effective partial sessiontransfer procedure in an IP layer or lower layers of the IP layerwithout having to deliver signaling to an IMS layer, and a UE for thesame.

Technical Solution

According to an aspect of the present invention, a partial sessiontransfer method for a user equipment establishing a first session totransmit a plurality of media components is provided. The methodincludes: transmitting a partial attach request message to a mobilitycontrol entity of a network core; receiving an attach accept messageincluding information regarding a gateway of the network core from themobility control entity; establishing a second session with the gatewayby using the gateway information; and transmitting partial sessiontransfer information indicating a media component to be transmittedusing each of the first session and the second session among theplurality of media components.

In the aforementioned aspect of the present invention, After theestablishing of the second session, the first session may not bereleased but maintained without alteration. In addition, the pluralityof media components may be exchanged with a counterpart user equipmentthrough each of the first session and the second session on the basis ofthe partial session transfer information.

According to another aspect of the present invention, there is provideda user equipment including a processor configured to generate andprocess a message, and a first transceiver and a second transceiver,each of which is operatively connected to the processor to transmit themessage for the processor. The user equipment establishes a firstsession for transmitting a plurality of media components through thefirst transceiver. The processor is configured to generate a partialattach request message and deliver the partial attach request message tothe second transceiver. The second transceiver is configured to transmitthe delivered partial attach request message to a mobility controlentity of a network core, receive an attach accept message containinginformation regarding a gateway of the network core from the mobilitycontrol entity, and deliver the attach accept message to the processor.The processor is configured to establish a second session passingthrough the gateway and the second transceiver by using the gatewayinformation, generate partial session transfer information indicating amedia component to be transmitted using each of the first session andthe second session among the plurality of media components, and deliverthe partial session transfer information to the first transceiver and/orthe second transceiver. The first transceiver and/or the secondtransceiver are configured to transmit the delivered partial sessiontransfer information to a counterpart user equipment.

ADVANTAGEOUS EFFECTS

According to exemplary embodiments of the present invention, a partialsession transfer procedure is provided so that a seamless multimediaservice can be provided for a user equipment supporting a dual modeoperation even if session transfer is performed not for all multimediacomponents but for some media components. In particular, the partialsession transfer procedure is achieved through signaling in an Internetprotocol (IP) layer or lower layers of the IP layer, and thus there isno need to transmit a control signal up to an IP multimedia subsystem(IMS) layer. Therefore, unnecessary signaling up to the IMS layer can bedecreased, and an unnecessary procedure (e.g., registration procedure)can be omitted in an IMS stage.

DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic block diagram showing a structure of a wirelesscommunication system to explain a partial session transfer procedureaccording to an embodiment of the present invention.

FIG. 2 is a message flow diagram of a partial session transfer procedureaccording to a first embodiment of the present invention.

FIG. 3 is a message flow diagram of a partial session transfer procedureaccording to a second embodiment of the present invention.

MODE FOR INVENTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a schematic block diagram showing a structure of a wirelesscommunication system to explain a partial session transfer procedureaccording to an embodiment of the present invention.

Referring to FIG. 1, a wireless communication system includes a userequipment (UE) 10 and a network code 20. A radio access network (RAN) isprovided for communication between the UE 10 and the network core 20.Although communication between the UE 10 and the network core 20 isachieved via the RAN, the RAN is not shown in FIG. 1 for convenience ofexplanation. The structure of the RAN may differ according to acharacteristic or type of the UE 10 and/or the network core 20. Sincethe detailed structure is irrelevant to the present embodiment,descriptions thereof will be omitted.

The UE 10 is an apparatus for performing communication with a pluralityof network nodes and/or another UE through an RAN (e.g., an evolved-UMTSterrestrial radio access network (E-UTRAN)), and the term is notparticularly limited thereto. For example, the UE 10 may also bereferred to as a mobile station (MS), a user terminal (UT), a subscriberstation (SS), a wireless device (or a wireless station), etc. The UE 10may be mobile or fixed.

The UE 10 includes a processor 12 as a mean for signal generation andprocessing and transceivers 14 a and 14 b for transmitting/receiving aradio signal through the RAN. Although not shown, the UE 10 may furtherinclude a memory for storing user data or programs, a display unit fordisplaying a variety of information or data of the UE, and a userinterface (e.g., a keypad, a touch screen, etc.).

The UE 10 may support a multi-mode operation. For this, the UE 10includes at least two transceivers 14 a and 14 b. In a case where the UE10 includes a plurality of transceivers 14 a and 14 b, the processor 12operatively connected to the transceivers 14 a and 14 b also supportstheir operations. Further, the processor 12 receives or delivers signalsfrom each of the transceivers 14 a and 14 b. As shown in FIG. 1, theprocessor 12 and the transceivers 14 a and 14 b may be devices PS1 andPS2 devised to support packet switched (PS) communications.

The network core 20 includes a plurality of network nodes constituting acore of a PS communication system. The network core 20 may consist ofnetwork nodes of the PS communication system, such as an evolved packetcore (EPC). The EPC may be a general packet radio service (GPRS) system,a universal mobile telecommunications system (UMTS), or a 3^(rd)generation partnership project (3GPP) long term evolution (LTE) system.Only minimum possible network nodes are shown in FIG. 1 for descriptionpurposes, and thus the structure of the network core 20 is not limitedto the constitutional elements shown in FIG. 1.

The network core 20 includes a mobility control entity (i.e., a mobilitymanagement entity (MME) or a media access gateway (MAG)) 22 and agateway (GW) 24. The mobility control entity 22 performs severalfunctions of a control plane, for example, for processing a controlsignal when an attach request or a handover request is made from the UE.Further, the mobility control entity 22 performs functions such asevolved packet system (EPS) bearer, Internet protocol (IP) tunnelestablishment, mobility management, etc. The mobility control entity 22may be an MME of an enhanced universal mobile telecommunication system(E-UMTS) or an MAG, but this is for exemplary purposes only. The MAG isa network node defined in the Internet engineering task force (IETF) touse a proxy mobile Internet protocol (PMIP) which is a protocol relatedto mobility management of an IP level and user data transmission. TheMAC includes not only a mobility control plane but also a user dataplane.

The GW 24 is a network node that performs an input/output port functionto communicate with an external packet data network in the network core20. According to a specific attach procedure or a handover procedure,the UE 10 establishes an EPS bearer or an IP tunnel with up to the GW 24through the RAN. According to the embodiment of the present invention,the GW 24 also performs a function of releasing a pre-establishedmultimedia session and/or a session integration function. The GW 24 maybe a packet data network gateway (PDN GW) that is an edge gateway foraccessing to an external packet data network from the EPC.

The network core 20 may further include a home subscriber sever (HSS)and an authentication, authorization, and accounting (AAA) server 26.The HSS is a network node including a database containing subscriberinformation regarding a wireless communication system. The AAA server isan authentication-related server that allows the UE to access to anetwork node constituting the network core 20 and that provides controlby storing records such as a location of the UE. Although the HSS andthe AAA 26 are depicted as one block in FIG. 1, this is for explanationpurposes only. The HSS and the AAA 26 are logically identifiablefunctional entities. Physically, the HSS and the AAA 26 may beimplemented into one element or may be separately implemented.

Next, a partial session transfer procedure using the wirelesscommunication system of FIG. 1 according to an embodiment of the presentinvention will be described.

FIG. 2 is a message flow diagram of a partial session transfer procedureaccording to a first embodiment of the present invention. In FIG. 2, afirst UE (i.e., UE1) supporting a dual mode operation is currentlyproviding an IMS multimedia service by establishing a first multimediasession with a second UE (i.e., UE2) by the use of a first transceiver(i.e., PS1). To indicate the established first multimedia session, inFIG. 2, a multimedia bearer or an evolved packet system (EPS) bearer isprovided between the PS1 of the UE1 and a GW. A specific bearer ortunnel is also provided between the GW and the UE2. The IMS multimediaservice supports communication of a plurality of media components (i.e.,voice and non-voice media).

Referring to FIG. 2, the UE1 transmits a partial attach request messageto a network core, more specifically, a mobility control entity (i.e.,MME or MAG) of the network core, through a second transceiver (i.e.,PS2) (step S11). The mobility control entity may be the MME or the MAG.There is no restriction on reasons for the UE1 to transmit the partialattach request message UE1 through the PS2. For example, the UE1 maytransmit the partial attach request message through the PS2 when the UE1recognizes that the PS2 is available while using a multimedia servicethrough the PS1 and also when the UE1 determines that it is furthereffective to transfer some media components (e.g., voice media) of themultimedia service to the PS1. In this case, which media corresponds toa media component to be used in determination of effectiveness and to bea subject of transfer is irrelevant to the embodiment of the presentinvention.

The partial attach request message is a message for requesting accessfrom the UE1 PS2 to the network core for partial session transfer. Thereis no restriction on a format of the partial attach request message. Forexample, the partial attach request message may be an Attach Requestincluding information regarding an attach type which is set to a valueindicating ‘partial handover’. The Attach Request with such a format hasan advantage in that the attach type is distinguished from a previousAttach Request whose attach type is set to ‘initial attach’ or‘handover’. In addition, since it is sufficient to additionally provideonly an attach type of ‘partial handover’, the previous Attach Requestcan be used without alteration. Several network nodes (e.g., MME (orMAG), GW, HSS, AAA, etc.) constituting the network code adaptivelyperform operations according to the attach type information contained inthe Attach Request.

Upon receiving the partial attach request message from the PS2 of theUE2, the mobility control entity (i.e., MME or MAG) performs anauthentication procedure on the UE1 by accessing an HSS and an AAA (stepS12). A detailed process of the authentication procedure may differaccording to a type of the network core and/or a radio access network(RAN), and is performed according to a typical procedure.

After successfully performing the authentication procedure, the mobilecontrol entity (i.e., MME or MAG) performs a location update procedure(step S13). The location update procedure is performed when the mobilitycontrol entity (i.e., MME or MAG) accessing through the PS2 is differentfrom a previously used entity, that is, a mobility control entityaccessing through the PS1.

After performing the location update procedure, the mobility controlentity (i.e., MME or MAG) performs a procedure for obtainingsubscriber's data from the HSS (step S14). For this, the HSS deliversthe subscriber's data to the mobility control entity. In this case, thesubscriber's data contains information regarding all access point names(APNs) usable by the UE1 together with information regarding the GW,i.e., an IP address of the GW. Through such a procedure, the HSS and theAAA assign a GW for the UE1 PS2 and report information thereon to themobility control entity (i.e., MME or MAG).

If the attach type is ‘partial attach’, the same GW as that previouslyassigned for the UE1 PS1 can be assigned for the UE1 PS2. This ispossible because the HSS and the AAA have information regarding the GWcurrently assigned to the UE1 PS1. However, the embodiment of thepresent invention is not limited thereto, and thus the GW assigned forthe UE1 PS2 may be a new GW different from the previous GW. In thiscase, the IP address of the newly assigned GW and information thereonare stored in the HSS and the AAA, which will be described below withreference to FIG. 3. The mobility control entity (i.e., MME or MAG) alsoupdates information regarding the UE1 PS2 newly added to the context ofthe previous UE1.

Next, a procedure for establishing a new bearer or tunnel for partialsession transfer is performed between the mobility control entity (i.e.,MME or MAG) and the GW (steps S15 and S16).

For this, the mobility control entity transmits a bear establishmentrequest message or a tunnel establishment request message to the GW viaa serving GW (step S15). The bearer establishment request message may beCreate Default Bearer Request. The tunnel establishment request messagemay be (P)MIP Binding Update. These message types are for exemplarypurposes only.

In response thereto, the GW transmits a bear establish response messageor a tunnel establish response message to the mobility control entity(step S16). The bear establish response message may be Create DefaultBearer Response. The tunnel establish response message may be (P)MIPBinding Ack. Together with acknowledgment or non-acknowledgment on thereceived request message, the response message includes a tunnelendpoint identifier (TEID) or an IP address of a network node forreporting the GW that is an end point of a tunnel or a newly establishedbearer.

As such, a variety of information determined by the HSS is included inthe response message transmitted in step S16. In particular, for a newpartial session of the UE1, information (e.g., GW IP information)regarding a GW assigned for the UE1 PS2 is included. As in the presentembodiment, the GW information may be IP information of the same GW asthat previously used by the UE1 PS1, or as described below, may be IPinformation of a newly assigned GW different from the previous GW.

Subsequently, the mobility control entity (i.e., MME or MAG) transmitsAttach Accept to the UE1 (step S17). The Attach Accept includes a TEIDor an IP address of a network node for establishing an EPS bearer or anIP tunnel. More specifically, the Attach Accept is transmitted from themobility control node to the UE1 PS2 through the RAN, whereas the IPaddress or the TEID included in the Attach Accept are transmitted up toa node of the RAN.

Next, a radio bear establishment procedure is performed between the UE1PS2 and the RAN, and a bear or tunnel establishment procedure isperformed between the RAN and the GW, so that a new session (e.g., a newEPS bearer or an IP tunnel) is established between the UE1 PS2 and theGW (step S18). According to the embodiment of the present invention, theUE1 PS1 maintains a previous EPS bearer or IP tunnel (e.g., a previouslyestablished multimedia bearer before step S11 of FIG. 2) establishedwith the GW instead of releasing the previous EPS or IP tunnel. This isbecause, according to the embodiment of the present invention forpartial session transfer, only some of media components are transmittedthrough a newly established EPS bearer or IP tunnel, and the remainingmedia components are transmitted through the previous EPS bearer.

Subsequently, although not shown, a GW which has established a new EPSbearer with the UE1 PS2 performs a new bearer or tunnel establishmentprocedure with a counterpart UE (i.e., UE2) and/or a wirelesscommunication system (i.e., network core, RAN, etc.) including thecounterpart UE (i.e., UE2). Such a procedure is performed according to atypical bearer establishment procedure, and thus detailed descriptionsthereof will be omitted. However, if the GW is the same as the GW whichhas established the EPS bearer with the UE1 PS1, a new EPS bearer or IPtunnel establishment procedure between the GW and the UE2 can beomitted.

As such, when the new bearer or tunnel establishment procedure iscompleted between the UE1 PS2 and the GW, the UE1 has two EPS bearsand/or IP tunnels that can be used by up to the GW. In this case, theUE1 determines a media component to be transmitted through a newlyestablished bearer (or tunnel) independently from the multimediacomponents through the partial session transfer, or determines mediacomponents to be transmitted through the two bearers (or tunnels),respectively, among the multimedia components. For example, among themultimedia components, the UE1 may make a decision so that non-voicemedia is exchanged through a previous bearer, i.e., a bearer (or tunnel)established through the UE1 PS1, and voice media is exchanged through anewly established bearer, i.e., a bearer (or tunnel) established throughthe UE1 PS2.

Further, the UE1 delivers information containing such a decision result,i.e., partial session transfer information, to a counterpart UE (i.e.,UE2), a network core of the counterpart UE (i.e., UE2), or an entity forproviding a multimedia service. Alternatively, the UE1 delivers theinformation to the counterpart UE (i.e., UE2) and a wirelesscommunication system of the counterpart UE (i.e., UE2) including anentity for providing a service (step S19). There is no restriction on amethod of delivering the partial session transfer information by the UE1to the counterpart UE (i.e., the UE2). For example, the UE1 may deliverthe partial session transfer information to the UE2 by using only theprevious bearer or the newly established bearer or by using both of thetwo established bearers.

Referring continuously to FIG. 2, the UE1 exchanges multimedia data withthe GW through the established two EPS bearers or IP tunnels (step S20).As described above, in the present embodiment, since the same GW isassigned to the UE1 PS1 and the UE1 PS2, multimedia data transmissionperformed in step S20 is also achieved through the same GW. However,similarly to a second embodiment of the present invention to bedescribed below with reference to FIG. 3, when different GWs areassigned to the UE1 PS1 and the UE1 PS2, multimedia data transmission isalso achieved through the different GWs.

In this step, a media component to be transmitted through each EPSbearer or IP tunnel is determined according to partial session transferinformation previously transmitted to the counterpart UE. For example,according to the partial session transfer information delivered in stepS19, non-voice data may be exchanged through the previous EPS bearer(i.e., the EPS bearer established through the UE1 PS1), and voice datamay be exchanged through the newly established EPS bearer (i.e., the EPSbearer established through the UE1 PS2). Multimedia data is transmittedthrough any path (e.g., a pre-established bearer or two bearers) fromthe GW to the counterpart UE (i.e., UE2). Although it is shown in FIG. 2that the non-voice data and the voice data are transmitted throughseparate bearers, this is for exemplary purposes only.

FIG. 3 is a message flow diagram of a partial session transfer procedureaccording to a second embodiment of the present invention. In thepresent embodiment, a GW newly assigned for a UE1 PS2 for establishing anew multimedia bearer with a UE2 through partial session transfer is thesame as the first embodiment expect that the GW is a second GW (i.e.,GW2) which is different from a first GW (i.e., GW1) previously assignedfor the UE1 PS1. Hereinafter, the second embodiment will be described inbrief by focusing on the first embodiment described above with referenceto FIG. 2. The first embodiment can be equally applied unless specifiedotherwise in detail in the present embodiment.

Similarly to the first embodiment, in the second embodiment, a first UE(i.e., UE1) supporting a dual mode operation is currently providing anIMS multimedia service by establishing a first multimedia session with asecond UE (i.e., UE2) by the use of a first transceiver (i.e., PS1). Toindicate the established first multimedia session, in FIG. 3, amultimedia bearer or an evolved packet system (EPS) bearer is providedbetween the PS1 of the UE1 and the first GW (i.e., GW1). A specificbearer or tunnel is also provided between the GW1 and the UE2. The IMSmultimedia service supports communication of a plurality of mediacomponents (i.e., voice and non-voice media).

Referring to FIG. 3, the UE1 transmits a partial attach request messageto a network core, more specifically, a mobility control entity (i.e.,MME or MAG) of the network core, through a second transceiver (i.e.,PS2) (step S31). The partial attach request message is a message forrequesting access from the UE1 PS2 to the network core for partialsession transfer. There is no restriction on a format of the partialattach request message. For example, the partial attach request messagemay be Attach Request including information regarding an attach typewhich is set to a value indicating ‘partial handover’.

Upon receiving the partial attach request message from the PS2 of theUE2, the mobility control entity (i.e., MME or MAG) performs anauthentication procedure on the UE1 by accessing to an HSS and an AAA(step S32). After successfully performing the authentication procedure,the mobile control entity (i.e., MME or MAG) performs a location updateprocedure (step S33). Subsequently, the mobility control entity (i.e.,MME or MAG) performs a procedure for obtaining subscriber's data fromthe HSS (step S34). The subscriber's data contains information regardingall access point names (APNs) usable by the UE1 together withinformation regarding the GW, i.e., an IP address of the second GW(i.e., GW2). Through such a procedure, the HSS and the AAA assign theGW2 that is a GW for the UE1 PS2 and report information thereon to themobility control entity (i.e., MME or MAG). As such, in the presentembodiment, the GW2 which is a different GW from the GW1 previouslyassigned for the UE1 PS1 is assigned for the UE1 PS2.

Next, a procedure for establishing a new bearer or tunnel for partialsession transfer is performed between the mobility control entity (i.e.,MME or MAG) and the GW2 (steps S35 and S36). For this, the mobilitycontrol entity transmits a bear establishment request message or atunnel establishment request message to the GW2 via a serving GW (stepS35). In response thereto, the GW2 transmits a bear establish responsemessage or a tunnel establish response message to the mobility controlentity through the serving GW (step S36). Together with acknowledgementor non-acknowledgment on the received request message, the responsemessage includes a TEID or an IP address of a network node for reportingthe GW2 that is an end point of a tunnel or a newly established bearer.As described above, the TEID or the IP address of the GW2 may bedifferent from the TEID or the IP address of the GW1.

Subsequently, the mobility control entity (i.e., MME or MAG) transmitsAttach Accept to the UE1 (step S37). The Attach Accept includes a TEIDor an IP address of the GW2 that is a network node for establishing anEPS bearer or an IP tunnel. Then, a radio bear establishment procedureis performed between the UE1 PS2 and the RAN, and a bear or tunnelestablishment procedure is performed between the RAN and the GW2, sothat a new session (e.g., a new EPS bearer or an IP tunnel) isestablished between the UE1 PS2 and the GW2 (step S38). According to theembodiment of the present invention, the UE1 PS1 maintains a previousEPS bearer or IP tunnel (e.g., a previously established multimediabearer before step S31 of FIG. 3) established with the GW1 instead ofreleasing the previous EPS or IP tunnel.

Further, the UE1 delivers information containing a decision result on atype of a media component to be transmitted through each EPS bearer,i.e., partial session transfer information, to a counterpart UE (i.e.,UE2), a network core of the counterpart UE (i.e., UE2), or an entity forproviding a multimedia service. Alternatively, the UE1 delivers theinformation to the counterpart UE (i.e., UE2) and a wirelesscommunication system of the counterpart UE (i.e., UE2) including anentity for providing a service (step S39). There is no restriction on amethod of delivering the partial session transfer information by the UE1to the counterpart UE (i.e., the UE2). For example, the UE1 may deliverthe partial session transfer information to the UE2 by using only theprevious bearer or the newly established bearer or by using both of thetwo bearers.

Referring continuously to FIG. 3, the UE1 exchanges multimedia data withthe UE2 by using the established two EPS bearers or IP tunnels throughthe GW1 and the GW2, respectively (step S40). As described above, in thepresent embodiment, since different GWs are assigned to the UE1 PS1 andthe UE1 PS2, the UE1 PS1 and the UE1 PS2 respectively transmit differentmedia components through the GW1 and the GW2. In the multimedia data,types of media components transmitted through the respective GWs can bedivided corresponding to the partial session transfer informationdelivered in step S39.

Although the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention as defined by the appended claims.

1. A partial session transfer method for a user equipment establishing afirst session to transmit a plurality of media components, the methodcomprising: transmitting a partial attach request message to a mobilitycontrol entity of a network core; receiving an attach accept messageincluding information regarding a gateway of the network core from themobility control entity; establishing a second session with the gatewayby using the gateway information; and transmitting partial sessiontransfer information indicating a media component to be transmittedusing each of the first session and the second session among theplurality of media components.
 2. The partial session transfer method ofclaim 1, wherein, after the establishing of the second session, thefirst session is not released but is maintained without alteration. 3.The partial session transfer method of claim 2, further comprisingexchanging the plurality of media components with a counterpart userequipment through each of the first session and the second session onthe basis of the partial session transfer information.
 4. The partialsession transfer method of claim 1, wherein the partial attach requestmessage is an attach request message including attach type informationindicating a partial handover.
 5. The partial session transfer method ofclaim 1, wherein a gateway for the second session is identical to agateway for the first session.
 6. The partial session transfer method ofclaim 1, wherein a gateway for the second session is different from agateway for the first session.
 7. The partial session transfer method ofclaim 1, wherein the user equipment supports a dual mode operation, andwherein the user equipment establishes the second session through aradio access network different from a radio access network to which thefirst session is established.
 8. The partial session transfer method ofclaim 1, wherein the gateway information is a tunnel endpoint identifier(TEID) or an Internet protocol (IP) address of the gateway.
 9. A userequipment comprising: a processor configured to generate and process amessage; and a first transceiver and a second transceiver, each of whichis operatively connected to the processor to transmit the message forthe processor, wherein the user equipment establishes a first sessionfor transmitting a plurality of media components through the firsttransceiver, the processor is configured to generate a partial attachrequest message and deliver the partial attach request message to thesecond transceiver, the second transceiver is configured to transmit thedelivered partial attach request message to a mobility control entity ofa network core, receive an attach accept message containing informationregarding a gateway of the network core from the mobility controlentity, and deliver the attach accept message to the processor, theprocessor is configured to establish a second session passing throughthe gateway and the second transceiver by using the gateway information,generate partial session transfer information indicating a mediacomponent to be transmitted using each of the first session and thesecond session among the plurality of media components, and deliver thepartial session transfer information to the first transceiver and/or thesecond transceiver, and the first transceiver and/or the secondtransceiver are configured to transmit the delivered partial sessiontransfer information to a counterpart user equipment.